Position calculation method and position calculation device

Abstract

In a position calculation device, an inertial navigation arithmetic unit calculates the position, the velocity, and the posture angle of the device by performing inertial navigation arithmetic using a detection value of an IMU, and a Kalman filter unit presumptively calculates the position, the velocity, the posture angle, or the like of the device by performing Kalman filter processing using an arithmetic result of the inertial navigation arithmetic unit. In addition, a KF initial parameter setting unit sets an initial value of an error covariance matrix which is an error index value used in the Kalman filter processing according to a difference with respect to an environment of the previous use.

What is claimed is: 
     
         1 . A position calculation method, comprising:
 executing first position calculation processing which estimates and updates an error index value relevant to a detection value of a sensor by using the detection value of the sensor, and calculates a position at a first time point;   storing environment information at the time of calculating the first position calculation processing; and   executing second position calculation processing which sets an initial error index value at the time of performing position calculation at a second time point later than the first time point on the basis of a difference between environment information at the second time point and the stored environment information at the first time point, estimates and updates the error index value by using the detection result of the sensor, and calculates a position at the second time point.   
     
     
         2 . The position calculation method according to  claim 1 ,
 wherein the first position calculation processing and the second position calculation processing are processing which calculates a position by using a Kalman filter using an error covariance matrix based on the error index value.   
     
     
         3 . The position calculation method according to  claim 1 , further comprising:
 setting the initial error index value at the time of performing the position calculation at the second time point to an error index value indicating a predetermined maximum error when the difference between the environment information at the second time point and the environment information at the first time point does not satisfy predetermined acceptable difference conditions, and the sensor is not calibrated.   
     
     
         4 . The position calculation method according to  claim 3 , further comprising:
 performing the position calculation at the second time point by setting a bias error of the sensor to zero when the initial error index value is the error index value indicating the maximum error.   
     
     
         5 . The position calculation method according to  claim 1 ,
 wherein the environment information includes information of an environmental temperature of the sensor, and   the setting the error index value includes variably setting the error index value according to a difference between an environmental temperature at the second time point and an environmental temperature at the first time point.   
     
     
         6 . The position calculation method according to  claim 1 ,
 wherein the storing includes storing calculated date and time of the first position calculation processing, and   the setting the initial error index value includes variably setting the initial error index value according to a difference between the date and time at the time of newly performing the position calculation and the stored calculated date and time.   
     
     
         7 . A position calculation device, comprising:
 a sensor;   a position calculation unit which estimates and updates an error index value relevant to a detection value of the sensor, and calculates a position at a first time point; and   a setting unit which stores environment information at the time of performing position calculation at the first time point by the position calculation unit in a storage unit, and sets an initial error index value at the time of performing the position calculation at a second time point later than the first time point on the basis of a difference between environment information at the time of performing the position calculation at the second time point and environment information at the first time point stored in the storage unit.